为什么说领导部门的出现是秘书工作起源的条件之一。

.

–Did you see ____ English teacher? 

--I saw him at ____ work in the office just now.

A．an, /

B．the, a

C．the, /

D．the, the

After a two-hour talk, she______ the truth of the report.

A. was persuaded                       B. was believed in 

C. was convinced of                     D was advised

用NA表示阿伏加德罗常数，下列说法正确的是（  ）

A．0.1mol的Na₂O₂中含阴离子数是2N_A

B．14g乙烯和丙烯的混合物中含有的碳原子数为N_A

C．1mol的溴乙烷中含有N_A个Br­-

D．1mol乙酸和1mol无水乙醇反应生成的乙酸乙酯分子为N_A

某工程双代号时标网络计划如下图所示，其中工作E的自由时差为（）周。

A．0

B．1

C．2

D．3

简述停用呼吸机的指征。